Device and method for treating skin

ABSTRACT

A system and method for heating a tissue volume under a skin surface of an individual from an initial temperature to a predetermined treatment temperature in the range of 42°-60° C. The method comprises applying electrodes to the skin surface and providing from the electrodes a continuous wave RF energy or a quasi-continuous wave RF energy, where the RF energy has a power selected to heat the tissue volume to the final temperature in an amount of time exceeding 0.5 sec. The system of the invention comprises electrodes and an RF generator configured to provide a continuous wave RF voltage energy or a quasi-continuous wave RF voltage across the electrodes where the RF energy has a power selected to heat the tissue volume to the final temperature in an amount of time exceeding 0.5 sec.

FIELD OF THE INVENTION

This invention relates to methods and devices for treating skin.

BACKGROUND OF THE INVENTION

There are many medical and cosmetic treatments of skin that utilizeheating a region of skin to be treated. Among these are hair removal,treatment of vascular lesions and skin rejuvenation. In thesetreatments, a volume of skin tissue under the skin to be treated isheated to a temperature that sufficiently high to achieve a desiredeffect, which is typically in the range of 45-60° C. One method that hasbeen used for heating the epidermal and dermal layers of the skin ispulsed radio-frequency (RF) energy. In this method, electrodes areapplied to the skin and an RF voltage pulse is applied across theelectrodes. The properties of the voltage pulse are selected so as togenerate an RF current pulse in the tissue to be treated that heats thetissue to the required temperature. For example, U.S. Pat. No. 6,749,626discloses use of pulsed RF energy for inducing collagen formation in thedermis.

When an RF current pulse is used to heat a volume of skin tissue, thetemperature of the tissue volume rises from body temperature to therequired temperature within the duration of the pulse, which istypically less than 100 msec. The temperature of the tissue volume thusrises vary rapidly. Since the final temperature will actually depend onthe electrical properties of the tissue volume which vary fromindividual to individual, the rapid rise in temperature of the tissuevolume limits control of the tissue heating. Moreover, the rapid rise intemperature prevents the user from stopping the treatment should thetissue volume become overheated. Thus, using an RF pulse to heat theskin carries a risk of overheating the skin which could result inpermanent scarring or other damage to the skin surface. Such damage tothe skin includes, for example, a first degree or higher burn, blisters,or blood coagulation.

SUMMARY OF THE INVENTION

The present invention provides a method and system for heating a tissuevolume under a skin surface. In accordance with the invention an RFcurrent is generated in a tissue volume to be treated that heats thetissue volume to a desired temperature in a period of time that exceeds0.5 sec. The slow rise in temperature allows the user to control theskin temperature and to avoid overheating of the skin. The invention isparticularly useful for skin treatments requiring the tissue volume tobe heated to a temperature in the range of 42° C. to 60° C. Suchtreatments include, for example, skin rejuvenation, collagen remodelingand contraction, skin tightening, wrinkle treatment, subcutaneous tissuetreatment, cellulite treatment, pore size reduction, skin texture andtone improvement, acne treatment and hair removal.

In one embodiment of the invention, a pair of RF electrodes are appliedto the skin surface, and an RF energy pulse is applied to the skinsurface having a duration and power selected so as to heat the skinsurface to a predetermined treatment temperature within an amount oftime exceeding 0.5 sec. For example, an RF energy pulse having a powerrange of 2-10 Watts could be used. In this case a pulse duration of0.5-1 sec would heat the tissue volume to a temperature in the range of45°-60° C. within 0.5-2 sec. The electrodes could be positioned at afirst location in a skin region to be treated and the RF energy pulseapplied to the first location. The electrode pair could then berepositioned on the skin surface to another location in the region to betreated and the procedure repeated. In another embodiment of theinvention, continuous wave (CW) RF energy is applied to the skin surfaceand by a pair of electrodes which are displaced over the skin surface.The power of the CW RF energy and the displacement speed are selected sothat each of a plurality of successive tissue volumes are heated to thepredetermined treatment temperature in a time that exceeds 0.5 sec asthe electrodes pass on the skin surface over the tissue volume. Forexample, CW RF energy having a power range of 2-10 Watts could be used.In this case, a displacement speed of about 0.5 -1.0 cm/sec would heat atissue volume under the electrodes to a temperature in the range of42°-60° C. in a time that exceeds 0.5 sec. Quasi-CW RF energy may alsobe used in which a train of RF pulses is applied to the skin surface,where the train has a frequency and the pulses have durations andpowers, so as to heat the tissue volume to be treated to a predeterminedtemperature in a period of time that exceeds 0.5 sec.

The system of the invention comprises a two or more RF electrodes and anRF generator configured to apply an RF voltage across at least a pair ofelectrodes, where the RF voltage has a power selected to heat a tissuevolume to a predetermined treatment temperature in a time period thatexceeds 0.5 sec., when an electrode pair is applied to the skin surfaceover the tissue volume. The RF generator may be configured to deliver apulse of RF energy having a duration exceeding 0.5 sec. Alternatively,the RF generator could be configured to deliver CW or quasi-CW RF energyto the electrodes, in which case, the electrodes are displaced over theskin surface during delivery of the RF energy. In a preferred embodimentof the system, a pair of RF electrodes are included in a hand heldapplicator. A user treating his own skin with the system of theinvention may simply displace the applicator over the skin surface inthe region to be treated at a speed at which the user feels that theskin is heated but not to an extent that causes pain to the user.

The slow heating of the skin volume by the method and system of theinvention permits greater control of the tissue heating, and thusreduces the risk of overheating, and hence damaging, the tissue.

Thus, in its first aspect, the invention provides a system for heating atissue volume under a skin surface of an individual from an initialtemperature to a predetermined treatment temperature in the range of42°-60° C., comprising:

-   -   (a) an applicator;    -   (b) a first electrode and a second electrode, at least the first        electrode being associated with the applicator; and    -   (c) An RF generator configured to provide a continuous wave RF        voltage energy or a quasi-continuous wave RF voltage across the        first and second electrodes, the RF voltage selected to heat the        tissue volume to the treatment temperature in a time period        exceeding 0.5 sec.

In its second aspect, the invention provides a method for heating atissue volume under a region of a skin surface of an individual from aninitial temperature to a predetermined treatment temperature, thetreatment temperature being in the range of 42°-60° C., comprising, foreach of one or more locations in the region of the skin surface:

-   -   (a) applying a first electrode and a second electrode to the        skin surface, at least the first electrode being applied to the        location in the skin region;    -   (b) providing from the electrodes a continuous wave RF energy or        a quasi-continuous wave RF energy to the tissue volume at the        location, the RF energy having a power selected to heat the        tissue volume at the location to the final temperature in an        amount of time exceeding 0.5 sec.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 shows a system for treating skin in accordance with oneembodiment of the invention;

FIG. 2 shows the applicator of the system of FIG. 1; and

FIG. 3 shows the electrodes of the applicator of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system 1 for treating skin in accordance with oneembodiment of the invention. The system 1 includes a hand heldapplicator 2 that is used to apply RF energy to the skin of anindividual 4. The applicator 2 is connected to a control unit 6 via aharness 8. The control unit 6 includes an RF generator 10 that generatesa continuous wave, or quasi-continuous RF voltage across a pair ofelectrodes 12 and 14 in the applicator 2. The control unit 10 includesan input device such as a key pad 11 for selecting the wavelength andamplitude of the RF voltage generated by the RF generator 10 as requiredin any particular skin treatment. The RF generator is connected to theelectrodes 12 and 14 by a pair of wires in the harness 8. The system 1may be plugged into a wall electrical socket 9, as shown in FIG. 1 oruse batteries (not shown) that are preferably rechargeable.

FIGS. 2 and 3 show the applicator 2 in greater detail. The applicator 2contains a push-button on-off switch 16. The switch 16 is spring biasedin an open position, so that no voltage is applied to the electrodes 12and 14 when the switch 16 is released. When the applicator 2 is held bya user, as shown in FIG. 1, the switch 16 is depressed and a continuousor quasi-continuous wave RF voltage is applied between the electrodes 12and 14. The electrodes 12 and 14 preferably have rounded edges in orderto avoid hot spots on the skin surface in the vicinity of the edges ofthe electrodes. Rounded electrodes also allow smooth moving of the handpiece over the skin surface. A uni-polar electrode system may also beused (not shown).

The applicator 2 preferably, though not necessarily, includes a lightsource 21 which is located between the electrodes 12 and 14 thatgenerates optical energy that is directed to the skin 25 surface by areflector 24. Optical energy directed to the skin surface from the lightsource 21 is used to specifically heat pigmented targets at the skinsurface. Such skin targets include vascular lesions, varicose veins,acne, and mole marks. The optical energy may have a single wavelength orseveral wavelengths. The wavelengths are selected to be optimal for thecolor of the contrasted component of the target, and are typically inthe range of 400 to 1800 nm. A filament lamp or gas filled lamp can beused as the light source 21. Light from a laser or LED also can be usedfor skin irradiation.

In use, the applicator 2 is held by the user and the electrodes 12 and14 are applied to the skin. The switch 16 is then depressed so as todeliver a continuous wave RF current to a section 17 of the skin betweenthe electrodes 12 and 14. The applicator 2 is displaced over the skin ina skin region 15 to be treated so as to heat the skin region to atemperature that produces the desired treatment of the skin.

The displacement velocity of the applicator 2 over the skin isdetermined so that the skin section between the electrodes is heated toa temperature that produces the desired skin treatment, but does notdamage the skin. Damage to the skin may include, for example, a firstdegree or higher burn, blisters, or blood coagulation. The displacementspeed of the applicator over the skin will thus be a function of thecontinuous RF power. As the RF power increases, the movement of theapplicator over the skin surface should be faster in order to avoid skindamage due to overheating of the skin.

The desired displacement speed can be determined, for example, using theequation ${V = \frac{P}{L\quad d\quad c\quad{\rho\Delta}\quad T}},$where P is the power of the continuous RF current, L is the spacing ofthe electrodes, d is the penetration depth of the RF energy, c is thespecific heat of the treated tissue, ρ is the mass density of thetissue, and ΔT is the required temperature increase starting from aminitial temperature equal to normal body temperature (about 37-39° C.).Thus, for example, if the RF power is P=5 W, the spacing of theelectrodes is L=1 cm, the RF penetration depth is d=0.25 cm, cp=4J/cm³/°K and ΔT=10° C., the applicator displacement speed should beabout 0.5 cm/sec. in order to achieve the desired heating in amount oftime in slightly more than 0.5 sec. If a mono-polar electrode system isused, the power should be lower to avoid damage to sub-dermal tissue.

A user treating his own skin with the system of the invention may simplydisplace the applicator over the skin surface in the region to betreated at a speed at which the user feels that the skin is heated butnot to an extent that causes pain to the user. Alternatively, thecontrol unit 6 may include a processor 7 that monitors the impedance ofthe skin between the electrodes 12 and 14. Since increasing skintemperature leads to a change in impedance, monitoring the skinimpedance allows the temperature in the skin between the electrodes tobe followed, as is known in the art. If the processor 7 determines thatthe skin temperature is below the range that is required to produce thedesired skin treatment (for example, 45° C. to 60° C., which maybe inputto the processor prior to the treatment), the processor may generate asensible signal, such as sounding an alarm 13 at a first pitchindicating to the user that the displacement speed should be decreased.Similarly, if the processor determines that the skin temperature is toohigh and may damage the skin, the processor can produce a secondsensible signal, such as sounding the alarm 13 at a second pitchindicating to the user that the displacement speed should be increased.

The system 1 may be used with the following exemplary parameter values:

An RF power in the range of 2-10 Watts.

An energy delivery mode that is CW or Quasi-CW

An RF frequency in the range of 0.2-10 MHz

An optical energy spectrum in the range of 400-1800 nm

Optical energy power in the range of 1 to 20 Watts/cm²

1. A system for heating a tissue volume under a skin surface of anindividual from an initial temperature to a predetermined treatmenttemperature in the range of 42°-60° C., comprising: p1 (a) anapplicator; (b) a first electrode and a second electrode, at least thefirst electrode being associated with the applicator; and (c) An RFgenerator configured to provide a continuous wave RF voltage energy or aquasi-continuous wave RF voltage across the first and second electrodes,the RF voltage selected to heat the tissue volume to the treatmenttemperature in a time period exceeding 0.5 sec.
 2. The system accordingto claim 1 wherein the first and second electrodes are associated withthe applicator.
 3. The system according to claim 2 wherein the RFvoltage has a power in the range of 2-10 W.
 4. The system according toclaim 1 wherein the RF voltage has a frequency in the range of 0.2-10MHz.
 5. The system according to claim 1 wherein the applicator furthercomprises a light source configured to direct optical energy to the skinregion.
 6. The system according to claim 5 wherein the optical energyhas a spectrum in the range of 400-1800 nm.
 7. The system according toclaim 5 wherein the optical energy has an energy power in the range of 1to 10 W
 8. The system according to claim 5 wherein the light source isselected from an incandescent lamp, a gas filled lamp, a LED and alaser.
 9. The system according to claim 1 further comprising a processorconfigured to determine a heat distribution in the skin based upon oneor more impedance measurements.
 10. The system according to claim 1wherein the processor is configured to generate a sensible signal if theskin temperature is below a predetermined temperature.
 11. The systemaccording to claim 10 wherein the sensible signal is sounding an alarmat a first pitch.
 12. The system according to claim 1 wherein theprocessor is configured to generate a sensible signal if the skintemperature is above a predetermined temperature.
 13. The systemaccording to claim 12 wherein the sensible signal is sounding an alarmat a second pitch.
 14. The method according to claim 1 wherein theinitial temperature is normal body temperature.
 15. A method for heatinga tissue volume under a region of a skin surface of an individual froman initial temperature to a predetermined treatment temperature, thetreatment temperature being in the range of 42°-60° C., comprising, foreach of one or more locations in the region of the skin surface: (a)applying a first electrode and a second electrode to the skin surface,at least the first electrode being applied to the location in the skinregion; (b) providing from the electrodes a continuous wave RF energy ora quasi-continuous wave RF energy to the tissue volume at the location,the RF energy having a power selected to heat the tissue volume at thelocation to the final temperature in an amount of time exceeding 0.5sec.
 16. The method according to claim 15 further comprising displacingat least the first electrode in the skin region at a displacement speedselected to heat the tissue volume the final.
 17. The method accordingto claim 16 wherein the first and second electrodes are displaced overthe skin region.
 18. The method according to claim 17 wherein the firstand second electrodes are spaced apart by a fixed distance L and thefirst and second electrodes are displaced over the skin surface at adisplacement speed given by the algebraic expression${V = \frac{P}{L\quad d\quad c\quad{\rho\Delta}\quad T}},$ where P isthe power of the RF current d is a penetration depth of the RF energy, cis a specific heat of the treated tissue, p is a mass density of thetissue, and ΔT is the required temperature increase.
 19. The methodaccording to claim 16 wherein the RF energy has a power in the range of2-10 W.
 20. The method according to claim 16 wherein the RF power has afrequency in the range of 0.2-10 MHz.
 21. The method according to claim16 further comprising illuminating the skin region with optical energy.22. The method according to claim 20 wherein the optical energy has aspectrum in the range of 400-1800 nm.
 23. The method according to claim20 wherein the optical energy has an energy power in the range of 1 to10 W
 24. The method according to claim 20 wherein the light source isselected from an incandescent lamp, a gas filled lamp, a LED and alaser.
 25. The method according to claim 16 further comprisingdetermining a temperature at one or more locations in the skin region.26. The method according to claim 25 wherein the temperature isdetermined based upon one or more impedance measurements between theelectrodes.
 27. The method according to claim 17 further comprisingincreasing the displacement speed when the skin temperature at alocation is below a predetermined temperature range.
 28. The methodaccording to claim 16 further comprising generating a first sensiblesignal if the skin temperature is below a predetermined temperature. 29.The method according to claim 28 wherein the first sensible signal issounding an alarm at a first pitch.
 30. The method according to claim 17further comprising decreasing the displacement speed when the skintemperature at a location is above a predetermined temperature range.31. The method according to claim 16 further comprising generating asecond sensible signal if the skin temperature is above a predeterminedtemperature.
 32. The method according to claim 31 wherein the secondsensible signal is sounding an alarm at a second pitch.
 33. The methodaccording to claim 16, wherein the skin treatment is selected from skinrejuvenation, collagen remodeling and contraction, skin tightening,wrinkle treatment, subcutaneous tissue treatment, cellulite treatment,pore size reduction, skin texture and tone improvement, acne treatmentand hair removal.
 34. The method according to claim 15 wherein theinitial temperature is normal body temperature.